1. Field
The present invention relates to a wireless communication system, and more particularly to an apparatus for feeding back channel information considering interference according to an access of a additional terminal and a technology for switching between a Single User-Multiple Input Multiple Output (SU-MIMO) mode allowing an access of a single User Equipment (hereinafter, referred to as a “UE”) and a Multiple User-Multiple Input Multiple Output (MU-MIMO) mode allowing accesses of multiple users at the same time by using the apparatus.
2. Discussion of the Background
With the development of a communication system, consumers such as enterprises and individuals have used highly various wireless terminals.
In current mobile communication systems such as current 3GPP, LTE (Long Term Evolution), and LTE-A (LTE Advanced), it is required to develop a technology, which can transmit high capacity data, equivalent to a wired communication network as a high speed and capacity communication system, which can transmit and receive various data such as image, radio data, etc. beyond services mainly for voice. Further, it is necessary for such a technology to have a proper error detecting method, which can minimize an information loss and increase a system efficiency thereby improving a system capability.
Meanwhile, both transmitting and receiving sides adopt a communication system using MIMO (multiple-Input Multiple-Output) antennas, and the communication system has a structure in which a Single UE (SU) or Multiple UEs (MU) share the same capacity of radio resources and receive or transmit a signal from or to one base station.
Meanwhile, a communication scheme such as 3GPP requires a process of grasping a channel state by using several reference signals and feeding back the grasped channel state to another device.
That is, when one UE is allocated a plurality of downlink physical channels, the UE may feedback channel state information for each physical channel to a base station to adaptively optimize a system. To this end, a Channel Status Index-Reference Signal (CSI-RS), a is Channel Quality Indicator (CQI) signal, and a Precoding Matrix Index (PMI) signal may be used. The base station can use the channel state related information to schedule a channel.
Meanwhile, when another UE attempts an access in an SU-MIMO environment, the SU-MIMO does not consider interference which all UEs including a currently accessed UE and the UE to be accessed will experience due to the UE attempting the access. Accordingly, the UE cannot receive the support of appropriate performance when a system converts the SU-MIMO mode to the MU-MIMO or the system is operated in the MU-MIMO.
That is, the switching from the SU-MIMO mode to the MU-MIMO mode causes the existing UE to have performance deterioration due to the interference generated by the newly accessed UE, and also causes the newly accessed UE to have communication performance deterioration due to the interference between the existing UE and the newly accessed UE.